It’s become an annual ritual: Congress can’t agree on a budget, so it adopts a “continuing resolution” to keep the government funded.

Here’s a guide to this mammoth spending bill and how it came about:

Q. What is a continuing resolution?

A. Legislation to keep the government running. Congress is supposed to adopt a budget by first agreeing to a broad outline in the spring, then adopting spending bills, each dealing with a different subject. The work is supposed to be done by Oct. 1, the start of the fiscal year.

For decades, Congress has routinely failed to meet that deadline. So it agrees to continue funding for the government, usually at or near the previous year’s levels, in a “continuing resolution.”

Q. How long does it keep the government funded?

A. It can provide money for a day, a week, or for the rest of the year. In fiscal 2001, Congress passed 21 CRs.

Q. Suppose some of the individual spending bills are adopted in time?

A. That often happens, and the areas they cover aren’t included in the resolution.

Q. Why don’t government officials like CRs?

A. Individual spending bills come from subcommittees and committees where lawmakers hear testimony and are familiar with the agencies. They know where money can be best spent and saved. A CR is usually a general approach to funding, and its temporary nature makes it hard for agencies to plan and strategize.

Q. What if neither the spending bills nor the CR passes before the funding runs out?

A. Much of the government shuts down. The record is the 21-day partial closing in 1995-96. This year a shutdown will occur if a new CR is not adopted by March 27.

Q. Are any government functions excepted?

A. Yes, government activities that involve “the safety of human life or the protection of property,” such as national security, continue. In addition, entitlement benefits, such as Social Security and much of Medicare, are not included, nor is interest on the debt.

Q. How are those benefits funded?

A. By law, they continue automatically.

Q. Are continuing resolutions something new?

A. No. From fiscal 1952 to 1976, when fiscal years began July 1, they were necessary because at least one spending bill was not adopted on time. In 1976, the start of the fiscal year was moved to Oct. 1, so lawmakers would have more time to debate and adopt spending legislation.

Q. Did that work?

A. Briefly. By the early 1980s, federal budget deficits had ballooned, Ronald Reagan was elected with a pledge to dramatically pare the government, and spending legislation began dominating Washington debate. Spending debates got bigger and more contentious. Instead of legislation that was a page or two, the CR ballooned to 363 pages by 1985.

Q. Why is Congress considering a CR now?

A. Because last year, it could not agree on spending. Rather than engage in a pre-election slugfest, it agreed in September to put off the debate until well after the election, and adopted a CR to fund the government through March 27 at fiscal 2012 levels, though many programs could get a 0.612 percent increase.

Q. What will the new CR do?

A. Specifics remain unclear, since the House and Senate versions will differ. The House of Representatives passed its bill Wednesday, the Senate plans to act next week, and then a negotiating committee will try to iron out a compromise. The final agreement is likely to set spending levels at $984 billion for the rest of this year and continue funding most agencies at last year’s levels, minus the automatic spending cuts, or sequester, that took effect March 1.

Q. Will the sequester continue?

A. Yes, but it could be tweaked. The Republican-led House wants to make changes in military and veterans funding, while Democrats are talking about doing the same for more domestic programs.

Q. Is another CR likely for the fiscal year that begins in October?

A. History suggests yes. The House and Senate are expected to adopt their own versions of budget outlines by April 15, but chances they will agree on one plan don’t seem good. Then they have to settle on the dozen spending bills by Oct. 1. That rarely happens.